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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Understanding the Mechanism Stabilizing Intermediate Spin States in Fe(II)-Porphyrin
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Understanding the Mechanism Stabilizing Intermediate Spin States in Fe(II)-Porphyrin

机译：了解稳定中间旋转状态的机制 - II（II）-纯蛋白

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Spin fluctuations in Fe(II)-porphyrins are at the heart of heme-proteins functionality. Despite significant progress in porphyrin chemistry, the mechanisms that rule spin state stabilization remain elusive. Here, it is demonstrated by using multiconfigurational quantum chemical approaches, including the novel Stochastic-CASSCF method, that electron delocalization between the metal center and the pi system of the macrocycle differentially stabilizes the triplet spin states over the quintet. This delocalization takes place via charge-transfer excitations, involving the it system of the macrocycle and the out-of-plane iron d orbitals, key linking orbitals between metal and macrocycle. Through a correlated breathing mechanism the 3d electrons can make transitions toward the pi orbitals of the macrocycle. This guarantees a strong coupling between the on-site radial correlation on the metal and electron delocalization. Opposite-spin 3d electrons of the triplet can effectively reduce electron repulsion in this manner. Constraining the out-of-plane orbitals from breathing hinders delocalization and reverses the spin ordering. The breathing mechanism is made effective by strong electron correlation effects in the pi system of the macrocycle. Reducing the correlation treatment on the macrocycle to second-order only also reverses the spin ordering. High order (beyond second-order) correlation on the macrocycle reduces the energetic cost of the additional electron to a sufficient extent to stabilize the triplet state. Our results find a qualitative analogue in six resonance structures involving the metal center in the Fe2+ and Fe3+ oxidation states.
机译：Fe（II）-纯卟啉的旋转波动是血红素蛋白功能的核心。尽管在卟啉化学方面取得了重大进展，但规则旋转状态稳定的机制仍然难以捉摸。这里，通过使用多组件量子化学方法来证明，包括新型随机烧焦方法，金属中心和宏细胞的PI系统之间的电子临床化差异稳定在QUINTET上的三联旋转状态。这种临床化通过电荷转移激发发生，涉及宏观的IT系统和平面外铁D轨道，金属和宏循环之间的关键连接轨道。通过相关的呼吸机理，3D电子可以向宏循环的PI轨道进行过渡。这保证了在金属和电子临床化上的现场径向相关之间的强烈耦合。三联体的相对旋转3D电子可以以这种方式有效地降低电子排斥。约束平面外轨道呼吸阻碍临床化并逆转旋转排序。通过宏循环PI系统中的强电子相关效果有效地实现了呼吸机理。降低宏观循环对二阶的相关处理也仅逆转旋转排序。宏观上的高阶（超出二阶）相关性降低了额外电子的能量成本，以足够程度地稳定三重态状态。我们的结果在涉及Fe2 +和Fe3 +氧化态中的六个共振结构中找到了一个定性模拟。

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